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Why does this Query return NULL?

I have a derby users database which I query, when the user clicks login on the application.
However, when I query the users table with the parameter [user] derby returns a null Object instead of the record it ought to return.
Here is my code:
String ssql = "SELECT * FROM USERS WHERE UNAME LIKE ?";
try{
DriverManager.registerDriver(new org.apache.derby.jdbc.EmbeddedDriver());
con = DriverManager.getConnection(url);
sql = con.prepareStatement(ssql, Statement.RETURN_GENERATED_KEYS);
sql.setString(1, cbox_chooseUser.getSelectedItem().toString());
sql.executeQuery();
ResultSet rs = sql.getGeneratedKeys();
try{
while (rs.next()) {
if(rs.getString("PW").toCharArray().equals(txt_password.getPassword())){
sql.close();
con.close();
return true;
}
} catch (NPE ...) {...}
}
I tried it multiple times wit a test user with both the pw and the username set to "test"; but I always get the same error.
Why is the recordset always Null?
Thanks for your help :)

The documentation says
ResultSet getGeneratedKeys() throws SQLException
Retrieves any auto-generated keys created as a result of executing this Statement
object.
If this Statement object did not generate any keys, an empty
ResultSet object is returned.
Your select statement isn't generating any keys that's why it's returning an empty ResultSet. You aren't inserting anything hence no keys are being generated.
You can try ResultSet rs = sql.executeQuery();. It should work.

You are using it in wrong way.
The generated keys concept should be used only in the case DML of insert type query but not in the case of select query.
select simply select the rows from the table. In this case there is no chance of any keys getting generated.
In the case of insert query if any column is configured as auto increment or kind of functionality then some keys will get generated. These keys can be caught using Statement.RETURN_GENERATED_KEYS in java.
As you are using select query there is no need of using Statement.RETURN_GENERATED_KEYS.
You just modify below lines and everything will be fine.
sql = con.prepareStatement(ssql, Statement.RETURN_GENERATED_KEYS);
sql.setString(1, cbox_chooseUser.getSelectedItem().toString());
sql.executeQuery();
ResultSet rs = sql.getGeneratedKeys();
with
sql = con.prepareStatement( ssql );
sql.setString( 1, cbox_chooseUser.getSelectedItem().toString() );
ResultSet rs = sql.executeQuery();

inserting byte array into blob column

I'm trying to insert byte array into a blob column in sqlite database. I've tried with both setBinaryStream and setBytes, but I'm getting not implemented by SQLite JDBC driver exception. I'm using sqlite-jdbc-3.8.7.jar.What jar should I use to get this work? Thanks!
Here's my code:
public void addDriverData(String prenume,String nume,String telefon,String email,String permis,String parola,byte[] photo) throws SQLException
{ String sql = "INSERT INTO driver(first_name,last_name,phone,email,permit,password,photo)VALUES(?,?,?,?,?,?,?)";
PreparedStatement stm = c.prepareStatement(sql);
stm.setString(1,prenume);
stm.setString(2,nume);
stm.setString(3,telefon);
stm.setString(4,email);
stm.setString(5,permis);
stm.setString(6, parola);
//stm.setBinaryStream(7,new ByteArrayInputStream(photo),photo.length);
stm.setBytes(7, photo);
System.out.println(sql);
stm.executeUpdate(sql);
stm.close();
c.commit();
}

Once a PreparedStatement object has been created with
String sql = "INSERT INTO ...";
PreparedStatement stm = c.prepareStatement(sql);
the object has already processed the sql command text. When the time comes to execute the PreparedStatement all we need to do is
stm.executeUpdate();
(The method call executeUpdate(sql) is intended to be used with Statement objects, not PreparedStatement objects.)

SQL insert into Quotes wrong

int rs = stmt.executeUpdate("INSERT INTO Leden VALUES (null,"+u+","+p+",'1')");
I'm getting the error
java.sql.SQLException: Unknown column '(the U variable)' in 'field list';
I know for sure it is 100% the "" but i can't seem to find it where it goes wrong
any help is appreciated!
This is my whole method (I want to learn how to do it with a prepared statement)
public static void connectionDB(String u, String p, String f){
{
try {
String username = "/////////";
String password = "///////";
String url = "///////////////";
Connection connection = DriverManager.getConnection(url, username, password);
Statement stmt = connection.createStatement();
int rs = stmt.executeUpdate("INSERT INTO Leden VALUES (null,'"+u+"','"+p+"','1')");
} catch (SQLException e) {
e.printStackTrace();
}
System.out.println("Database connected!");
}
}

It should be like
int rs = stmt.executeUpdate("INSERT INTO Leden VALUES (null,'"+u+"','"+p+"','1')");
Update:-
You can also look into prepared statements because
Prepared statements are much faster when you have to run the same statement multiple times, with different data. Thats because SQL will validate the query only once, whereas if you just use a statement it will validate the query each time.
Assuming fields are A,B,C,D;
A is int and remains are strings
String insertTableSQL = "INSERT INTO Leden"
+ "(A,B,C,D) VALUES"
+ "(?,?,?,?)";
preparedStatement.setInt(1, 11);
preparedStatement.setString(2, "Hello");
preparedStatement.setString(3, "this");
preparedStatement.setString(4, "OP");]
preparedStatement .executeUpdate();

It should be
int rs = stmt.executeUpdate("INSERT INTO Leden VALUES (null,'"+u+"','"+p+"','1')'");

The issue is, that " is used in SQL for objects like columns or tables, whereas ' is used for strings. So in +u+, which seems to not exists in context of your query.
Your query itself should therefore look something like (given, that +u+ and +p+ are strings.
INSERT INTO Leden VALUES (null,'+u+','+p+','1')
If you need to have " inside your columns, it would read like
INSERT INTO Leden VALUES (null,'"+u+"','"+p+"','1')
Also I would recommend to specify the columns you are inserting to so it looks similar to:
INSERT INTO "Leden" ("col1", "col2", "col3", "col4") VALUES (null,'+u+','+p+','1')
This will prevent your query from failing when extending table definition by another column.
Also using prepared statements could be a good idea here, as it helps you preventing from e.g. SQL injections.

How to insert two strings into my Access database from Java using UCanAccess?

I am trying to add two strings on two separate columns columns of my database using Java but I'm not sure what I am doing wrong. The code I am using
try{
Connection conn = DriverManager.getConnection(
"jdbc:ucanaccess://C:/Users/nevik/Desktop/databaseJava/Employee.accdb");
Statement st = conn.createStatement();
String sql = "Select * from Table2";
ResultSet rs = st.executeQuery(sql);
rs.updateString("user", user);
rs.updateString("pass", pass);
rs.updateRow();
}
catch(SQLException ex){
System.err.println("Error: "+ ex);
}
The first column on my database is user and the next one is pass. I am using UCanAccess in order to access my database.

This is how you normally update a row in java:
String query = "update Table2 set user = ?, pass= ?";
PreparedStatement preparedStmt = conn.prepareStatement(query);
preparedStmt.setInt (1, user);
preparedStmt.setString(2, pass);
// execute the java preparedstatement
preparedStmt.executeUpdate();

First of, you've not updated the position of the current cursor in the ResultSet, which means that it's pointing to nothing...
You could use...
if (rs.next()) {
rs.updateString("user", user);
rs.updateString("pass", pass);
rs.updateRow();
}
But this assumes two things...
You have a database that supports updating values in the ResultSet and
You want to update the existing values.
To insert a value into the database, you should be using the INSERT command, for example...
try(Connection conn = DriverManager.getConnection(
"jdbc:ucanaccess://C:/Users/nevik/Desktop/databaseJava/Employee.accdb")) {
try (PreparedStatement stmt = conn.prepareStatement("INSERT into Table2 (user, pass) VALUES (?, ?)") {
stmt.setString(1, user);
stmt.setString(2, pass);
int rowsUpdated = stmt.executeUpdate();
}
}
catch(SQLException ex){
System.err.println("Error: "+ ex);
}
You might like to take some time to go over a basic SQL tutorial and the JDBC(TM) Database Access trail
As a side note...
You should not be storing passwords in Strings, you should keep them in char arrays and
You should not be storing passwords in the database without encrypting them in some way

#guevarak12
About the original question (how to use updatable ResultSet):
your code is wrong, you have to move the cursor in the right position.
In particular, if you are inserting a new row you have to call rs.moveToInsertRow(); before rs.updateString("user", user).
If you are updating an existent row, you have to move the cursor calling rs.next() and so reach the row to update.
Also you have to create the Statement in a different way:
Statement st =conn.createStatement( ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_UPDATABLE);
See junit examples in the UCanAccess source distribution, class net.ucanaccess.test.CrudTest.
All other comments seem to be correct.

Is there a way to retrieve the autoincrement ID from a prepared statement

Is there a way to retrieve the auto generated key from a DB query when using a java query with prepared statements.
For example, I know AutoGeneratedKeys can work as follows.
stmt = conn.createStatement();
stmt.executeUpdate(sql, Statement.RETURN_GENERATED_KEYS);
if(returnLastInsertId) {
ResultSet rs = stmt.getGeneratedKeys();
rs.next();
auto_id = rs.getInt(1);
}
However. What if I want to do an insert with a prepared Statement.
String sql = "INSERT INTO table (column1, column2) values(?, ?)";
stmt = conn.prepareStatement(sql);
//this is an error
stmt.executeUpdate(Statement.RETURN_GENERATED_KEYS);
if(returnLastInsertId) {
//this is an error since the above is an error
ResultSet rs = stmt.getGeneratedKeys();
rs.next();
auto_id = rs.getInt(1);
}
Is there a way to do this that I don't know about. It seems from the javadoc that PreparedStatements can't return the Auto Generated ID.

Yes. See here. Section 7.1.9. Change your code to:
String sql = "INSERT INTO table (column1, column2) values(?, ?)";
stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
stmt.executeUpdate();
if(returnLastInsertId) {
ResultSet rs = stmt.getGeneratedKeys();
rs.next();
auto_id = rs.getInt(1);
}

There's a couple of ways, and it seems different jdbc drivers handles things a bit different, or not at all in some cases(some will only give you autogenerated primary keys, not other columns) but the basic forms are
stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
Or use this form:
String autogenColumns[] = {"column1","column2"};
stmt = conn.prepareStatement(sql, autogenColumns)

Yes, There is a way. I just found this hiding in the java doc.
They way is to pass the AutoGeneratedKeys id as follows
String sql = "INSERT INTO table (column1, column2) values(?, ?)";
stmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);

I'm one of those that surfed through a few threads looking for solution of this issue ... and finally get it to work. FOR THOSE USING jdbc:oracle:thin: with ojdbc6.jar PLEASE TAKE NOTE:
You can use either methods:
(Method 1)
Try{
String yourSQL="insert into Table1(Id,Col2,Col3) values(SEQ.nextval,?,?)";
myPrepStatement = <Connection>.prepareStatement(yourSQL, Statement.RETURN_GENERATED_KEYS);
myPrepStatement.setInt(1, 123);
myPrepStatement.setInt(2, 123);
myPrepStatement.executeUpdate();
ResultSet rs = getGeneratedKeys;
if(rs.next()) {
java.sql.RowId rid=rs.getRowId(1);
//what you get is only a RowId ref, try make use of it anyway U could think of
System.out.println(rid);
}
} catch (SQLException e) {
//
}
(Method 2)
Try{
String yourSQL="insert into Table1(Id,Col2,Col3) values(SEQ.nextval,?,?)";
//IMPORTANT: here's where other threads don tell U, you need to list ALL cols
//mentioned in your query in the array
myPrepStatement = <Connection>.prepareStatement(yourSQL, new String[]{"Id","Col2","Col3"});
myPrepStatement.setInt(1, 123);
myPrepStatement.setInt(2, 123);
myPrepStatement.executeUpdate();
ResultSet rs = getGeneratedKeys;
if(rs.next()) {
//In this exp, the autoKey val is in 1st col
int id=rs.getLong(1);
//now this's a real value of col Id
System.out.println(id);
}
} catch (SQLException e) {
//
}
Basically, try not used Method1 if you just want the value of SEQ.Nextval, b'cse it just return the RowID ref that you may cracked your head finding way to make use of it, which also don fit all data type you tried casting it to! This may works fine (return actual val) in MySQL, DB2 but not in Oracle.
AND, turn off your SQL Developer, Toad or any client which use the same login session to do INSERT when you're debugging. It MAY not affect you every time (debugging call) ... until you find your apps freeze without exception for some time. Yes ... halt without exception!

Connection connection=null;
int generatedkey=0;
PreparedStatement pstmt=connection.prepareStatement("Your insert query");
ResultSet rs=pstmt.getGeneratedKeys();
if (rs.next()) {
generatedkey=rs.getInt(1);
System.out.println("Auto Generated Primary Key " + generatedkey);
}